1. Field of the Invention
The present invention relates to an ink jet recording head for image recording by liquid emission and a driving circuit therefore, and more particularly to an ink jet recording head for achieving liquid emission by thermal energy, and a driving circuit therefor.
2. Related Background Art
Such an ink jet recording head has conventionally been prepared by forming, as shown in FIG. 1, liquid path forming members, a cover plate, etc. on a substrate having electrothermal converting elements, as disclosed for example in U.S. Pat. Nos. 4,410,899, 4,723,129, 4,417,251 and 4,509,063. Such an ink jet recording head is provided with plural liquid paths 3,3 . . . having orifices 2,2, . . . at the ends thereof; electrothermal converting elements 4,4, . . . ; and a common liquid chamber 5 communicating with said liquid paths.
FIG. 2 shows a driving circuit for such ink jet recording head, wherein said electrothermal converting elements 4,4, . . . are respectively connected to switching circuits 6,6, . . . which are selectively activated by a signal S.sub.on to supply an electric current to desired electrothermal converting elements 4,4, . . . to emit liquid ink from the orifices 2 as disclosed in U.S. Pat. Nos. 4,345,262 and 4,429,321.
However, such conventional ink jet recording head and driving circuit therefor may cause a problem when the electrothermal converting element of any of the liquid paths 3 is destructed. In such destructed state, the destructed electrothermal converting element 4 itself often contacts the ink in the liquid path, thus causing a current in the ink whereby the destructed heat-generating resistor has a capacitative component.
Consequently a square voltage wave applied in the normal state as shown in FIG. 3 will be distorted as shown in FIG. 4 in such destructed state.
As will be apparent from FIG. 4, the destructed electrothermal converting element will receive a voltage close to DC voltage, thus inducing an electrode reaction. In this manner the destruction of an electrothermal converting element 4 generates reaction products in the ink by the quasi-DC voltage, and such impurities in the ink composition may flow into other liquid paths through the common liquid chamber, thus clogging the orifices and the liquid paths and eventually deteriorating the performance of the entire recording head or totally disabling the recording head.